Isolation, detection and pharmacological activity of the major paraconic acids from Cetraria islandica

Paraconic acids are a group of secondary metabolites mainly found in lichens and selected fungi. Within this compound class, lichesterinic- and protolichesterinic acid have previously shown inhibitory activity on 5- and 12-lipoxygenase (LOX) [1], [2].

This compound class show weak UV-light absorption, resulting in a low sensitivity in (LC-)UV detection [3]. Moreover, their very similar structure makes their separation rather challenging. The present project describes a two-step isolation protocol to obtain the major paraconic acids from commercially available Cetraria islandica. First, the crude extract is separated by size exclusion chromatography to obtain fractions composed of isobaric compounds. Subsequently, lichesterinic- and protolichesterinic acid were separated by fast centrifugal partition chromatography, while roccelaric- and nephromopsinic acid were isolated by column chromatography. We also developed analytical methods to detect these compounds by thin layer chromatography (TLC), LC-MS, and LC-ELSD ([Fig. 1]).

Fig. 1 A Soxhlet extraction of C. islandica with petroleum ether. B Crystallization of paraconic acids after Soxhlet extraction. C TLC analysis. D Chemical structure of compounds contained in crystal mixture: nephromopsinic acid, 1; roccellaric 2; protolichesterinic acid, 3; lichesterinic acid, 4; nephrosteranic acid and an isomer, 5 and 6; nephrosterinic acid and an isomer, (7 and 8). E LC-MS analysis of petroleum ether extract of C. islandica after crystallization.

The effects of the paraconic acids on lipid mediator biosynthesis in human peripheral blood mononuclear cells (PBMC) were investigated by UPLC-MS/MS-based lipidomics. We found that paraconic acids diminished the mobilization of polyunsaturated fatty acids and thus lipid mediator biosynthesis (at 3 µM), potently interfere with 5-LOX product formation (at 3 µM) and elevate the levels of cytochrome P450 monooxygenase-derived epoxyeicosatrienoic acids (EETs) (at 30 µM).

In conclusion, we managed the isolation of lichesterinic-, protolichesterinic-, roccellaric-, and nephromopsinic acid from Cetraria islandica with purities above 90%, which favorably shift the lipid mediator profile of activated innate immune cells from pro-inflammatory to anti-inflammatory products, while generally dampening lipid mediator production.

Publication History

Article published online:
12 December 2022

• References

• 1 Ingolfsdottir K, Breu W, Huneck S. et al. In vitro inhibition of 5-lipoxygenase by protolichesterinic acid from Cetraria islandica. Phytomedicine 1994; 1: 187-191
• 2 Bucar F, Schneider I, Ögmundsdóttir H, Ingólfsdóttir K. Anti-proliferative lichen compounds with inhibitory activity on 12(S)-HETE production in human platelets. Phytomedicine 2004; 11: 602-606
• 3 Xu M, Heidmarsson S, Thorsteinsdottir M, Kreuzer M. et al. Authentication of Iceland Moss (Cetraria islandica) by UPLC-QToF-MS chemical profiling and DNA barcoding. Food Chem 2018; 245: 989-996